1. Field of the Invention
The present invention relates to a zoom lens system, and in particular, relates to a zoom lens system that is favorable for use in a single-lens reflex camera.
2. Description of Related Art
Various zoom lens systems that are suitable for electronic still cameras have been proposed in the related art. For example, in each of Patent Literature Nos. 1 through 3, a positive-lead zoom lens system configured of a positive lens group, a negative lens group, a positive lens group, a negative lens group and a positive lens group, in that order from the object side (five lens groups) is disclosed.
In such positive-lead zoom lens systems, the overall length of the zoom lens system can be made shorter at the wide-angle extremity (short focal length extremity) compared to that of a negative-lead zoom lens system. Furthermore, since a zoom lens system configured of five lens groups has additional freedom in regard to the movement of the lens groups thereof compared to that of a zoom lens system configured of four lens groups, fluctuation in aberrations that occur during zooming can be suppressed.
On the other hand, in recent zoom lens systems for use in a digital single-lens reflex camera, a high optical quality is demanded over the entire focal length range (zooming range).
Generally, in a zoom lens system, when the refractive power of a lens group that takes the major burden of the zooming operation is increased, a high zoom ratio can be achieved with a predetermined movement amount of such a lens group; however, fluctuations in aberrations increase during zooming, making it difficult to achieve a favorable optical quality over the entire focal length range (zooming range).